1. Field of the Invention
The present invention relates to magnetic resonance diagnostic devices.
2. Description of the Prior Art
Magnetic resonance or spin imaging diagnostic devices generally include coils for generating a fundamental magnetic field and gradient fields in which an examination subject is disposed, and at least one measuring coil for monitoring the change of nuclear spin of the examination subject from an equilibrium position due to the magnetic excitation pulses. A device of this type is described, for example, in German OS No. 31 35 335. This device generates movement of the nuclear spin of the examination subject out of an equilibrium position maintained by the fundamental magnetic field by the application of a high-frequency excitation pulse. A signal is generated when the nuclear spin returns to normal at the end of the excitation pulse. Given precession of the nuclear spin, the frequency of the signal is dependent upon the strength of the fundamental magnetic field. If the uniform fundamental magnetic field is superimposed with a field gradient so that the magnetic field distribution varies three-dimensionally, locating by means of the measured frequency is made possible. Visible images of the examination subject can be generated in this manner and by modifying the direction of the respective field gradient. The excitation in a slice or layer of the examination subject is achieved by selecting a further field gradient for acting upon the fundamental magnetic field such that excitation of nuclear magnetic resonance occurs only in the layer of interest. This is possible because such excitation occurs only with a frequency which is precisely associated with the magnetic field in the selected layer.